1. Field of the Invention
The present invention relates to electrosensitive recording and recording media.
2. Description of the Prior Art
Electrosensitive recording materials typically have a base layer of paper that supports a resinous contrast coating on one side. A further coating of vapor-deposited metal, such as aluminum, covers the free surface of the resinous contrast coating. When electrical current is passed through a stylus in contact with the metallized surface, the metal is vaporized along the path of the stylus; this exposes the contrasting resinous layer. The resinous coating may include additives, such as matting agents to reduce the gloss of the metallized surface, and pigments or dyes to provide a pronounced contrast to the metallic surface where the latter has been removed.
Contemporary printers for electrosensitive material have the disadvantage that print quality hass not been as good as that obtained with competing printers. Another typical disadvantage has been the tendency to accumulate debris around the stylus, necessitating frequent shutdown of the printer for cleaning.
Many printers of this type have conductive grounding rollers which come into contact with the metallic surface of the electrosensitive material to provide electrical grounding for the material and possibly also to assist in feeding the electrosensitive material through the printer. When such printers are operated under high humidity conditions there is a tendency for microscopic portions of the metallic surface and underlying resinous coating layer to accumulate on the grounding rollers, ultimately leading to deterioration in print quality upon prolonged operation. The mechanism by which minor amounts of debris transfer to the ground rollers is not known with certainty. Occasional misfiring of the stylus because of a high metallic surface smoothness can be a contributing cause. It is also theorized that a retention of moisture on the metallic surface of the electrosensitive material occurring during operation in a high humidity environment especially when the metallic surface has a high degree of smoothness may increase friction or surface adhesion between the ground rollers and metallic surface aggravating the above problems.
In the development of electrosensitive paper for use as a recording medium in computer output printers, it has not heretofore been possible to produce a reasonably priced electrosensitive paper which could meet a large number of physical requirements. Among the most important properties of interest are tensile and tearing strength, burst strength, fingerprinting resistance, resistivity, barrier properties, minimal structural curling, matte appearance, print quality and limited production of debris during recording. It is also important that the electrosensitive paper not cause appreciable stylus wear.
Representative electrosensitive recording papers of the prior art comprise a paper base layer covered by a contrast layer of a lacquer coating or printing ink, which in turn is covered by metallic aluminum. Illustrative prior art patents include U.S. Pat. Nos. 3,786,518; 3,831,179; 3,995,083; 4,217,596; and 3,620,831; 2,833,677; 3,657,721; 3,861,952; and 4,024,546.
In U.S. Pat. No. 3,831,179 an intermediate contrast layer of cellulose-based lacquer is used to produce corrosion resistance and has good barrier properties in that it prevents moisture vapor from being transmitted through the paper base layer. This structure has the disadvantage that the contrast of the exposed resinous layer where the metallic surface is burned away is not satisfactory.
Numerous attempts have been made to improve the contrast between the recorded information and the outer metallic layer of the electorsensitive medium. Typically, carbon black pigment is added to the intermediate lacquer layer to produce a matting effect in an attempt to improve contrast. Such is the case in U.S. Pat. No. 3,995,083.
In U.S. Pat. No. 3,786,518, an amorphous silicon oxide additive is added to enhance the matte properties of the intermediate lacquer layer. This is to improve the contrast between the recorded information and an aluminum coating. Although amorphous silicon oxide reduces gloss so as to improve contrast, it alone does not prevent rapid buildup of debris around the stylus. Buildup of debris around the stylus detracts from print quality and necesssitates frequent shutdown of the printer for cleaning as noted in U.S. Pat. No. 4,217,596. Because of the disadvantages of silicon dioxide, an alternative additive is suggested in U.S. Pat. No. 4,217,596 in the form of a combustible organic matte-causing substance, preferably polysstyrene or polyethylene. The use of an organic, combustible matte-producing additive has the advantage over silicon oxide that practically no deposits will occur on the writing electrodes. Unlike silicon oxide, the organic matte-causing additive is burnt off upon recording. The result is very little, if any, residue around the electrodes. But organic matte-producing additives have the disadvantage of producing a diminished contrast.
Accordingly, it is a primary object of the present invention to provide electrosensitive recording media which permit prolonged operation of an electrosensitive printer. A related object is the avoidance of debris buildup on the stylii of such printers. It is particularly desirable to achieve these results under high humidity conditions.
It is another object of the present invention to provide improved contrast in electrosensitive recording materials.
A further object of the invention is to reduce the wear on the recording stylii used with electrosensitive materials.
Yet another object of the invention is to provide economical electrosensitive recording media satisfying an array of physical criteria, including for example printability, strength, and flexibility.